Organic EL devices are expected to see practical application in such fields as displays and lighting. Various research is being carried out on materials and device structures with the aim of achieving such properties as low-voltage driving, high brightness and good longevity.
A plurality of functional thin films are used in organic EL devices, one of which, the hole-injecting layer, is responsible for transferring charge between an anode and a hole-transporting layer or a light-emitting layer, and thus serves an important function in achieving low-voltage driving and high brightness in organic EL devices.
Processes for forming the hole-injecting layer are broadly divided into dry processes such as vapor deposition and wet processes such as spin coating. On comparing these processes, wet processes are better able to efficiently produce thin films having a high flatness over a large surface area. Therefore, particularly in the field of displays, wet processes are often used not only in the formation of the hole-injecting layer, but also in the formation of upper layers such as the hole-transporting layer and the light-emitting layer (see, for example, Patent Document 1).
In view of the above, the inventors have developed various charge-transporting varnishes that contain an aniline derivative as the charge-transporting substance (see, for example, Patent Documents 2 and 3). However, improvements continue to be desired in the wet process materials used to form the hole-injecting layer.
In particular, in order to be able to contribute to the brightness characteristics of the organic EL device, there is a desire for a higher uniformity not only in the hole-injecting layer, but also in the hole-transporting layer (see, for example, Patent Document 4). Hence, there exists a desire for a material which gives a charge-transporting thin film of excellent flatness and which, moreover, enables an excellent coatability to be achieved when forming a hole-transporting layer or light-emitting layer on this film by a wet process.